1. Field of the Invention
The invention relates generally to wafer transport systems within in-line sputtering systems and more particularly to a wafer transport system wherein wafer movement is induced by movement of a magnet exterior to the sputtering system process chambers.
2. Description of the Prior Art
In the semiconductor industry, systems for transporting wafers between process locations in a sputtering system are well known. Typically circular silicon wafers of various diameters are moved between positions at which metallic coatings are sputtered onto the wafer or at which etching occurs. This process takes place in a vacuum chamber in order to eliminate contamination of the wafer surface. The goal of all such transport systems is to move the wafer from one process location to another.
Some systems use a chain drive conveyor-belt type of transport system. Such a drive system must be totally within the area subject to vacuum conditions or the driving means must penetrate the chamber in which a vacuum is being maintained. Both methods have significant drawbacks in that space is wasted where the drive means is entirely within the vacuum chamber thereby increasing the chamber's volume and thus the time it takes to evacuate the chamber. In the case of penetration of the chamber, there exists the possibility of drawing contamination into the chamber due to the presence of atmospheric pressure at the penetration site. It also requires complex and costly sealing mechanisms to prevent such in flow of contamination through drive mechanism penetrations.
Other transport systems known in the art include rotating the wafers through process locations or using a geared mechanism which pushes wafers from one location to another by means of disks which contact the wafers.
In short, the known wafer transport systems all use drive means whether belts, chains, gears or sprockets, which are either located in the process chamber or which penetrate such process chambers. Where such means are used contamination problems are present due either to the materials present on the drive means or by imperfect sealing of such penetrations.
Many of the existing sputtering systems using the transport systems described above use pneumatic pedestals which lift a wafer off the wafer transport system and into a position for the processing of the wafer. In many cases the devices which support the wafer during transport are rigidly fixed to the movement means of the particular transport system. This permits the wafer support device to be damaged if it is improperly positioned over a pneumatic pedestal. In such a case, when the pedestal is raised, it strikes the support device damaging the pedestal, the support device or both. Also, systems with such rigidly fixed support devices cannot be readily adapted to carry wafers of various diameters. Delay is caused by having to disassemble the transport system and install new support devices for the new diameter wafers to be processed.